Recent developments in the avian sarcoma virus (ASV) system have allowed the isolation and identification of a 60,000 dalton phosphoprotein as the product of the ASV src gene. This gene product (termed pp60src) contains a protein kinase activity and most likely is directly involved in initiation and maintenance of host cell transformation. This research project proposes to investigate the mechanism of ASV-induced transformation by using pp60src as a direct probe of that mechanism. We plan to investigate the mechanism of ASV-induced transformation by using pp60src as a direct probe of that mechanism. We plan to investigate the intracellular location of pp60src by immunofluorescence in cells transformed by ASV mutants temperature sensitive for transformation and grown at permissive or nonpermissive temperature. Possible association with specific cellular molecules will be investigated by both biochemical and immunological means, and possible virus-host cell interactions within the src gene explored. In addition, the relationship of the endogenous chicken cell "sarc" pp60 to the viral pp60src will be studied, and these molecules compared with other endogenous "sarc" proteins found in uninfected rat and human cells. The natural function and metabolism of these endogenous sarc proteins will be investigated using both biochemical and immunological techniques. In addition to the ASV sarc gene product, another intriguing aspect of the transformed cell will be explored. This aspect deals with the expression of the ASV envelope antigen in mammalian cells transformed by this virus. Contrary to previous experimental results, current evidence suggests that the envelope antigen is expressed in transformed mammalian cells but in an antigenically altered form. Furthermore, viruses rescued from ASV-transformed mammalian cells display altered envelop antigens and are termed mammotropic ASV because they also exhibit an increased ability to transform mammalian cells. We plan to characterize the ASV envelope antigens expressed in these cells. Also, experiments have been designed to investigate the possible origin of the mammotropic character, and immunological consequences of the existence of altered envelope antigens in ASV transformed mammalian cells.